Monday, October 15, 2012

Nature: Mixed flu strain in Mizo man

Published online 15 October 2012

Researchers from the National Institute of Cholera and
Enteric Diseases (NICED) in Kolkata have spotted a classical case of
'sporadic reassortment' — mixing of genetic material from swine and
human origin viruses — in an influenza A viral strain with H1N2 subtype.1
The study supports the possibility of 'reassortment events' during
influenza season when infectivity is high and two different subtypes of
the virus circulate together in the same geographical location.
The mixed strain circulated during the swine flu pandemic in
2009-2010 and has been found from a 25-year-old man in Mizoram. The
strain has been named A/Eastern India/N-1289/2009.
Influenza A viruses of the H1N2 subtype were isolated previously in
India and Japan during 2001–02. They were reassortants of the human H1N1
and H3N2 viruses and distinct from the H1N2 swine influenza viruses.
However, repeated attempts to isolate the recombinant virus had failed.
The researchers say this could have been due to the 'loss of viability'
as the samples came from Mizoram (about 1219 kms from Kolkata) by
courier and took more than 48 hrs to reach the NICED lab.
Reassortment is responsible for some major genetic shifts in the
history of the influenza virus. The 1957 and 1968 pandemic flu strains
were caused by reassortment between an avian virus and a human virus.
The 2009 H1N1 swine flu virus has been found to have an unusual mix of
swine, avian and human influenza genetic sequences.
After sequencing the full genome, the researchers found the unique
reassortment event where the N-1289 virus acquired its hemagglutinin
(HA) gene from a 2009 pandemic H1N1 virus with swine origin and the
other genes from H3N2-like viruses of human origin.
Co-circulation of both these influenza viruses during 2009 and
complete disappearance of seasonal H3N2 and H1N1 strains in 2010 was
also observed in eastern India. Such co-circulation is the prime cause
of the generation of genetically reassortant viruses, the researchers
say.